New wound dressing compositions

ABSTRACT

A wound dressing composition comprising a non-viable cell lysate or releasate derived from a hepatocyte cell or an inflammatory cell such as a macrophage. Also provided are wound dressings comprising such compositions, methods of making such compositions, and the use of such compositions for the treatment of wounds.

The present invention relates to wound dressing compositions comprisinga non-viable cell lysate or releasate derived from macrophage orhepatocyte cells, to wound dressings comprising such compositions, tomethods of manufacture of such compositions and dressings, and to theuses of the compositions and dressings for wound healing.

All documents mentioned in the text are incorporated herein byreference.

U.S. Pat. No. 6,585,969 describes the use of cultured keratinocytesheets in wound healing. WO-A-2004050121 relates to a pharmaceuticalcomposition comprising a non-viable keratinocyte cell lysate and anantisedimentation agent. The effectiveness of these wound dressings canbe attributed to substances, such as growth factors, present in thecultured keratinocytes. Many known cytokines and growth factors, such asfibroblast growth factor (FGF), platelet derived growth factor (PDGF),epidermal growth factor (EGF), transforming growth factor alpha(TGF-alpha), transforming growth factor beta (TGF-beta) influencekeratinocytes and skin fibroblasts. For example, TGF-beta, EGF and FGFinduce keratinocyte proliferation. TGF-beta and PDGF stimulate thesynthesis of collagen and other connective tissue components. Because ofthese properties, such growth factors may play a role in promoting woundhealing and epidermal regeneration. Thus, the use of a cell culture or acell releasate or lysate which contains such growth factors may bebeneficial in promoting wound healing.

However, a problem with using such cell lysates to treat wounds is thatwounds contain proteases, which can degrade the useful growth factors.The level of endogenous proteases is especially elevated in chronicwounds, such as ulcers. Therefore the full effect of such lysates is notachieved.

The present inventors have found that a macrophage or hepatocyte cellreleasate/lysates promote fibroblast proliferation in vitro, even in thepresence of chronic wound fluid. It is thought that this effect may bedue to the presence in these lysates and releasates of proteaseinhibitors such as alpha-1-antitrypsin, in addition to growth factors.The effectiveness of these lysates and releasates as or in wounddressings is therefore expected to be greater than that of thekeratinocyte dressings described above.

Accordingly, in a first aspect the present invention provides a wounddressing composition comprising a non-viable cell lysate or releasatederived from a hepatocyte cell or an inflammatory cell.

Inflammatory cells include macrophages, monocytes, lymphocytes, mastcells, neutrophils, T-cells, and plasma cells. Suitably, theinflammatory cell is a macrophage cell. Macrophages are cells thatoriginate from specific white blood cells called monocytes. Macrophagesmature from monocytes produced in the bone marrow. Monocytes andmacrophages are phagocytes, acting in both non-specific defence as wellas cell-mediated immunity of vertebrate animals.

Hepatocytes make up 60-80% of the cytoplasmic mass of the liver. Thehepatocyte is the only cell in the body that manufactures albumin,fibrinogen and the prothrombin group of clotting factors. It is the mainsite for the synthesis of lipoproteins, transferrin, and glycoproteins.Hepatocytes manufacture their own structural proteins and intracellularenzymes.

The cell lysates and releasates used for the present invention maycomprise components from cells other than macrophages or hepatocytes.However, preferably at least about 1%, more preferably at least about10%, still more preferably at least about 30%, and most preferably about50% or more of the cells used to prepare the lysate or releasate aremacrophages and/or hepatocytes.

The term “cell lysate” refers to cell suspensions or fractions thereof,obtained by lysing the cells. The whole cell lysate contains allproteins and other molecules which were intended to remain intracellularand those intended to be secreted extracellularly. The cell lysatescomprise an extremely complex mixture of constituents such as proteins,glycoproteins, polysaccharides, lipids, nucleic acids etc. All thesecomponents may interact with each other. The cell lysate in the solutionor suspension of the present invention may comprise whole cells, partsof cells or any fractions or mixtures thereof obtained after a lysisstep. The term “cell releasate” refers to those proteins and othermolecules which are secreted extracellularly. Thus, the releasate can beregarded as a fraction of the lysate.

The cell lysate may be obtained from whole cells by any of the variouscell lysis processes which are well known to those skilled in the art.The term “cell lysis” refers to rupturing the cell wall and/or the cellmembrane of cells by a chemical, biological, mechanical or thermaltreatment. Numerous mechanical methods of lysis have been developed andpublished. They include pressure, cavitation, sonic or ultrasonic waves,mechanical shaking or grinding. Cell lysates may suitably be obtained bymechanically homogenizing the cells.

The hepatocyte or macrophage cell lysates of the present invention maypreferably be obtained by subjecting the cell suspension to multiplefreeze-thaw cycles, which disrupt the cell membrane thereby releasingthe cellular components into solution.

The whole cells may be primary isolates from human tissue, or the cellscan be obtained from a culture collection such as the European tissueculture collection or the American Tissue Culture Collection. Once avial of cells is bought/acquired they can be expanded and frozen stockmaintained indefinitely using normal cell culture techniques.

Useful cell lysate fractions may be obtained by lysing whole cells,subjecting the resulting lysate to centrifugation wherein certain partsof the resulting cell lysate are in the pellet fraction and certainother parts of the resulting cell lysate are in the supernatant.

The cell lysate is suitably prepared by lysing a cellular composition,such as an aqueous cellular suspension, containing more than about 2×10⁵cells/ml, for example from 0.25×10⁶ to about 5×10⁷ cells/ml, preferablyfrom about 0.5×10⁶ to about 1×10⁷ cells/ml. The concentration of thecell lysate in a composition of the present invention varies accordingto the type of cell lysate in the composition, as well as according toits intended use.

Releasates comprise proteins and other molecules, which the intact cellsecretes during its normal growth cycle. Thus, the releasate is asub-fraction of the cell lysate. The releasate is prepared by growingthe cells in vitro and harvesting the conditioned media at differenttimes, for example at 24 or 48 hours. The conditioned media contain theproteins, which the cells would normally secrete extracellularly inorder to carry out their specific functions. Suitably, the cells aregrown at a cell density of about 8×10⁶ cells/ml and releasates recoveredafter 24 hrs growth.

The cell releasates or lysates may be used directly, for example inaqueous suspension or in freeze-dried form. However, in mostcompositions according to the present invention the cell lysate orreleasate is dispersed in or on a pharmaceutically acceptable vehicle.The vehicle may be liquid, semi-solid (e.g. an ointment or a gel), orsolid. Preferably, the compositions of the invention are suitable fortopical application to a wound. Preferably, the compositions of theinvention are substantially sterile.

The liquid or semi-solid vehicles may be any such vehicle suitable forsupporting the cell lysate in the solution or suspension. Examples ofsuch liquid vehicles are water, oil, or emulsions (such as water-in-oilor oil-in-water emulsions) and other similar liquids.

The solid compositions according to the present invention may be in theform of gels, beads, flakes, powder, and preferably in the form of afilm, a fibrous pad, a web, a woven or non-woven fabric, a freeze-driedsponge, a foam, or combinations thereof. In certain embodiments, thematerial is selected from the group consisting of woven fabrics, knittedfabrics, and nonwoven fabrics, all of which may be made by conventionalmethods. In other embodiments, the material may comprise (or consistessentially of) a freeze-dried sponge or a solvent-dried sponge.

The solid vehicle may be bioabsorbable or non-bioabsorbable. The term“bioabsorbable ” refers to a material that is fully degraded andabsorbed in vivo in the mammalian body.

Suitable non-bioabsorbable materials include common textile materialssuch as cellulose, processed cellulose such as viscose, polyamide,polyurethane, and also alginates.

Suitable bioabsorbable materials include those selected from the groupconsisting of collagens, bioabsorbable cellulose derivatives such asoxidized celluloses, galactomannans such as guar/borate,glycosaminoglycans such as cross-linked hyaluronates, chitosans,polylactides and polyglycolide polymers and copolymers,polyhydroxybutyrates, and mixtures thereof.

Preferably, the solid composition according to the present inventioncomprises, or consists essentially of, a bioabsorbable freeze-driedsponge. Suitable methods of making freeze-dried and solvent-driedsponges are described in EP-A-1153622 and EP-A-0838491.

In certain preferred embodiments the vehicle comprises (and may consistessentially of) a solid bioabsorbable material selected from the groupconsisting of collagens, chitosans, oxidized celluloses, and mixturesthereof.

Oxidized cellulose is produced by the oxidation of cellulose, forexample with dinitrogen tetroxide. This process converts primary alcoholgroups on the saccharide residues to carboxylic acid group, forminguronic acid residues within the cellulose chain. The oxidation does notproceed with complete selectivity, and as a result hydroxyl groups oncarbons 2 and 3 are occasionally converted to the keto form. Theseketone units introduce an alkali labile link, which at pH7 or higherinitiates the decomposition of the polymer via formation of a lactoneand sugar ring cleavage. As a result, oxidized cellulose isbiodegradable and bioabsorbable under physiological conditions.

The preferred oxidized cellulose for practical applications is oxidizedregenerated cellulose (ORC) prepared by oxidation of a regeneratedcellulose, such as rayon. It has been known for some time that ORC hashaemostatic properties, and that application of ORC fabric can be usedto reduce the extent of post-surgical adhesions in abdominal surgery.

The oxidized regenerated cellulose (ORC) can be obtained by the processdescribed in U.S. Pat. No. 3,122,479. This material offers numerousadvantages including the features that it is biocompatible,biodegradable, non-immunogenic and readily commercially available. ORCis available with varying degrees of oxidation and hence rates ofdegradation. The ORC may be used in the form of insoluble fibers,including woven, non-woven and knitted fabrics.

Chitin is a natural biopolymer composed of N-acetyl-D-glucosamine units.Chitin may be extracted from the outer shell of shrimps and crabs inknown fashion. The chitin is then partially deacetylated, for example bytreatment with 5M-15M NaOH, to produce chitosan. Complete deacetylationof the chitin is not a practical possibility, but preferably thechitosan is at least 50% deacetylated, more preferably at least 75%deacetylated. Chitosan has been employed for wound treatment in variousphysical forms, e.g. as a solution/gel; film/membrane; sponge; powder orfiber. Chitosan in the free base form is swellable but not substantiallysoluble in water at near-neutral pH, but soluble in acids due to thepresence of ammonium groups on the chitosan chain. The solubility of thechitosan may be reduced by cross-linking, for example withepichlorhydrin. Typically, the average molecular weight of the chitosanas determined by gel permeation chromatography is from about 10⁵ toabout 10⁶.

The collagen useful as the solid substrate on the materials according tothe present invention may be any collagen, including Type I or Type IIor Type III collagen, natural fibrous collagen, atelocollagen, partiallyhydrolysed collagens such as gelatin, and combinations thereof.Recombinant human collagen, for example as described in U.S. Pat. No.5,962,648 and WO-A-2004078120 may be used. Natural fibrous collagen, forexample of bovine origin, is suitable. For example, the collagenprepared from bovine hide is a combination of Type I collagen (85%) andType III collagen (15%).

In certain embodiments of the present invention, the oxidized celluloseis complexed with collagen and/or chitosan to form structures of thekind described in WO98/00180, WO98/00446 or WO2004/026200. For example,the oxidized cellulose may be in the form of milled ORC fibres that havebeen dispersed in an aqueous suspension of collagen and thenfreeze-dried or solvent dried to form a bioabsorbable sponge. Thisprovides for certain therapeutic and synergistic effects arising fromthe complexation with collagen, as described in the above-referencedpatent specifications.

In particular embodiments, the polymeric substrate comprises (and mayconsist essentially of) a mixture of: (a) collagen and/or chitosan; and(b) oxidized regenerated cellulose, for example in a dry weight ratiorange of from about 90:10 to about 10:90 of collagen/chitosan:ORC,preferably from about 75:25 to about 25:75, and particularly from about60:40 to about 40:60.

The cell lysate or releasate is dispersed in and/or on the surface ofthe solid vehicle in a therapeutically effective concentration. That isto say, at a concentration that results in increased fibroblastproliferation relative to a control with no cell lysate or releasate, asdetermined by Procedure 1 below.

The solid wound healing compositions according to the present inventionare suitably substantially dry. In certain embodiments, they maycomprise up to about 20% by weight, preferably from about 2% to about10% by weight of water. The solid compositions according to the presentinvention may also contain 0-40% by weight, for example from about 5 toabout 25% by weight, of a plasticiser, preferably a polyhydric alcoholsuch as glycerol or sorbitol.

In certain embodiments, the wound healing compositions according to thepresent invention may also comprise up to about 10% by weight, forexample from about 0.01 to about 5% by weight, typically from about 0.1to about 2% by weight of one or more other wound healing therapeuticagents, such as non-steroidal anti-inflammatory drugs (e.g.acetaminophen), steroids, local anaesthetics, antimicrobial agents, orgrowth factors (e.g. fibroblast growth factor or platelet derived growthfactor). The antimicrobial agent may, for example, comprise anantiseptic, an antibiotic, or mixtures thereof. Preferred antibioticsinclude tetracycline, penicillins, terramycins, erythromycin,bacitracin, neomycin, polymycin B, mupirocin, clindamycin and mixturesthereof. Preferred antiseptics include silver, including colloidalsilver, silver salts including salts of one or more of the anionicpolymers making up the material, silver sulfadiazine, chlorhexidine,povidone iodine, triclosan, sucralfate, quaternary ammonium salts andmixtures thereof. The preferred antimicrobial agent is silver.Preferably, the amount of silver (as silver ions and metallic silver) inthe materials according to the present invention is from about 0.01 wt %to about 2 wt. %, more preferably from about 0.05 wt % to about 0.5 wt.%, and most preferably about 0.1 wt. % to about 0.3 wt. %. Lesseramounts of silver could give insufficient antimicrobial effect. Greateramounts of silver could give rise to antiproliferative effects on woundhealing cells.

All of the above percentages are on a dry weight basis.

In a second aspect, the present invention provides a wound dressingcomprising a wound dressing composition according to any precedingclaim.

The wound dressing composition in the dressing according to the presentinvention is typically in sheet or layer form, for example having anarea of from about 1 cm² to about 400 cm², in particular from about 2cm² to about 100 cm². The basis weight of the sheet is typically fromabout 100 g/m² to about 5000 g/m², for example from about 400 g/m² toabout 2000 g/m². The sheet of the composition according to the presentinvention forms an active layer of the dressing.

The said active layer in the dressings according to the invention wouldnormally be the wound contacting layer in use, but in some embodimentsit could be separated from the wound by a liquid-permeable top sheet.Preferably, the area of the active layer is from about 1 cm² to about400 cm², more preferably from about 4 cm² to about 100 cm².

The wound dressing may consist essentially of the active layer of thecomposition according to the present invention, in which case thedressing would normally be used in conjunction with a suitable secondarydressing. In other embodiments, the wound dressing according to theinvention further comprises a backing sheet extending over the activelayer opposite to the wound facing side of the active layer. Preferably,the backing sheet is larger than the active layer such that a marginalregion of width 1 mm to 50 mm, preferably 5 mm to 20 mm extends aroundthe active layer to form a so-called island dressing. In such cases, thebacking sheet is preferably coated with a pressure sensitive medicalgrade adhesive in at least its marginal region.

Preferably, the backing sheet is substantially liquid-impermeable. Thebacking sheet is preferably semipermeable. That is to say, the backingsheet is preferably permeable to water vapour, but not permeable toliquid water or wound exudate. Preferably, the backing sheet is alsomicroorganism-impermeable.

Suitable polymers for forming the backing sheet include polyurethanesand poly alkoxyalkyl acrylates and methacrylates such as those disclosedin GB-A-1280631. Preferably, the backing sheet comprises a continuouslayer of a high density blocked polyurethane foam that is predominantlyclosed-cell. A suitable backing sheet material is the polyurethane filmavailable under the Registered Trade Mark ESTANE 5714F.

The adhesive layer (where present) should be moisture vapourtransmitting and/or patterned to allow passage of water vapourtherethrough. The adhesive layer is preferably a continuous moisturevapour transmitting, pressure-sensitive adhesive layer of the typeconventionally used for island-type wound dressings. Polyurethane-basedpressure sensitive adhesives are preferred.

The wound dressing according to the present invention may furthercomprise an absorbent layer between the active layer and the backingsheet, especially if the dressing is for use on exuding wounds. Theoptional absorbent layer may be any of the layers conventionally usedfor absorbing wound fluids, serum or blood in the wound healing art,including gauzes, nonwoven fabrics, superabsorbents, hydrogels andmixtures thereof.

A removable cover sheet may protect the wound-facing surface of thedressing. The cover sheet is normally formed from flexible thermoplasticmaterial. Suitable materials include polyesters and polyolefins.Preferably, the adhesive- facing surface of the cover sheet is a releasesurface. That is to say a surface that is only weakly adherent to theactive layer and the adhesive on the backing sheet to assist removal ofthe cover sheet. For example, the cover sheet may be formed from anon-adherent plastic such as a fluoropolymer, or it may be provided witha release coating such as a silicone or fluoropolymer release coating.

Preferably, the wound dressing of the present invention is sterile andpackaged in a microorganism-impermeable container.

In a further aspect, the present invention provides a process for theproduction of a wound dressing composition comprising the steps of:lysing hepatocyte or macrophage cells to form a lysate, and dispersingthe lysate in or on a pharmaceutically acceptable carrier. Preferably,the wound dressing composition obtainable by the process of theinvention is a wound dressing composition according to the presentinvention as hereinbefore defined.

In certain embodiments, the concentration of protease inhibitors in thecells of the non-viable cell lysate or releasate is raised over thebasal level before the step of lysis. This is achieved by culturing thehepatocyte or macrophage cells in the presence of an agent selected fromthe group consisting of cytokines, bacterial endotoxins and exotoxins,and mixtures thereof. A suitable bacterial toxin for this purpose islipopolysaccharide derived from E. Coli.

In certain embodiments, the lysate or releasate is freeze-dried beforethe step of dispersing. The step of dispersing may be carried out bymixing or coating the substrate material with the cell lysate. Incertain embodiments, the lysate or releasate is mixed with an aqueousdispersion containing components of the solid substrate, and the mixtureis then freeze-dried or solvent dried to form a sponge containing thelysate or releasate.

In a further aspect, the present invention provides the use of anon-viable cell lysate or releasate derived from a hepatocyte cell, amacrophage cell, or mixtures thereof, for the preparation of amedicament for the treatment of a wound. Suitably, the medicament is awound dressing composition or a wound dressing as hereinbefore defined.

Suitably, the wound is a chronic wound. The compositions of theinvention are expected to be especially useful for the treatment ofchronic wounds because chronic wounds are known to exhibit elevatedendogenous protease levels, which contribute to the delayed healing ofthese wounds. Exemplary chronic wounds include venous ulcers, decubitisulcers and diabetic ulcers.

In a further aspect, the present invention provides a method oftreatment of a wound in a mammal, comprising the step of applying awound dressing composition according to the invention to the wound.Suitably, the wound is a chronic wound such as a decubitis ulcer, avenous ulcer or a diabetic ulcer.

Preferably, the dressing is applied to the chronic wound for a period ofat least 1-hour, more preferably at least 6 hours, and most preferablyat least 12 hours. The treatment may be extended for several days orweeks, with dressing changes as appropriate.

It will be appreciated that alternative or preferred features orembodiments that are described above in relation to any one aspect ofthe invention may also be applicable in any other aspect of theinvention.

Various aspects and embodiments of the present invention will now bedescribed in more detail by way of example, with reference to theaccompanying drawings, in which:

FIG. 1 shows the percentage of cell stimulation of normal human dermalcells (fibroblasts) when incubated in the presence of chronic woundfluid (samples (a) and (b))or acute wound fluid (sample (c));

FIG. 2 shows the percentage of fibroblast proliferation in dermal cellcultures incubated as follows (a) 10% serum as a positive control whichstimulates cells; (b) serum free media as a negative control whichmaintains cells but gives no growth; (c) chronic wound fluid alone; (d)media (solution) in which the releasate was prepared; (e) both thechronic wound fluid and a monocyte cell releasate; and (f) both thechronic wound fluid and the macrophage releasate; and

FIG. 3 shows the percentage of fibroblast proliferation in dermal cellcultures incubated as follows (a) 10% serum as a positive control whichstimulates cells; (b) serum free media as a negative control whichmaintains cells but gives no growth; (c) chronic wound fluid alone; and(d) both the chronic wound fluid and a macrophage cell lysate.

EXAMPLE 1 & EXAMPLE 2

Macrophage cell releasates and lysates were prepared as follows.

Monocyte/macrophage cells (THP-1 cells) obtained from a commercialsource were grown and maintained in cell culture media (RPMI 1640+2 mMGlutamine containing 10% FCS/FBS and 1% antibiotic/antimycotic). Thesecells are grown in suspension and are therefore routinely sub-culturedand used for experimental testing at a cell density of from 2 to 9×10⁵cells/ml. The cells were then harvested by centrifugation at 1000 rpmfor 10 mins. The pellet is then re-suspended in RPMI media containingPMA (phorbol ester—Phorbol 12-myristate 13-acetate) to give a finalconcentration of 2.5×10⁻⁷ M. This allows cells to become adherent anddifferentiated, i.e. to become macrophage-like. The cell suspensioncontaining PMA was then used to seed three 24 well microtitre plates ata cell density of 8×10⁶ cells/ml (i.e. 1 ml of cell suspension was addedto each well). The plates were then incubated at 37° C., 5% CO₂ for 24hours to allow adherence of cells to the tissue culture plastic.

The medium was then replaced by either RPMI+lipopolysaccharide (derivedfrom E. Coli, at 10 ng/ml) or RPMI alone, and allowed to grow for 24hours in a humidified incubator at 37° C., 5% CO₂. The addedlipopolysaccharide stimulates the production of the desired cytokines,growth factors, proteases and protease inhibitors by the cells. Theconditioned medium was then removed and labelled macrophage cellreleasate. The remaining cell monolayer was harvested and suspended at acell density of 1×10⁶ cells/ml, after which they subjected to 3freeze-thaw cycles in order to prepare a macrophage cell lysate.

EXAMPLE 3

Monocyte cell releasates were prepared as follows.

Monocyte/macrophage cells (THP-1 cells) obtained from a commercialsource were grown and maintained in cell culture media (RPMI 1640+2 mMGlutamine containing 10% FCS/FBS and 1% antibiotic/antimycotic). Thesecells are grown in suspension and are therefore routinely sub-culturedand used for experimental testing at a cell density 2-9×10⁵ cells/ml.The cells were then harvested by centrifugation at 1000 rpm for 10 mins.The pellet is then re-suspended in RPMI media and re-aliquoted at a celldensity of 8×10⁶ cells/ml. (i.e. 1 ml of cell suspension was added toeach tube). Lipopolysaccharide toxin derived from E. Coli was added tosome tubes (at 10 ng/ml in the RPMI medium) while others were left withRPMI medium alone; in all cases the cells were then incubated at 37° C.,5% CO₂ for 24 hours. The conditioned medium was then removed andlabelled monocyte cell releasate.

Procedure 1

The expected effects of cell lysates and releasates on wound healingwere studied in vitro as follows.

Incubating normal human dermal cells (fibroblasts) with chronic woundexudate (fluid) provides a model of a chronic wound. The ability of cellreleasate or lysate to overcome the negative effect of the chronic woundenvironment and stimulate cell growth was assessed in order to determinewhether cell releasate or lysate was able to stimulate healing in achronic wound.

Adult human dermal fibroblasts isolated from a male donor (ATCCCRL-2068) were grown and maintained in Dulbecco's Modified Eagle'sMedium (DMEM) containing 10% (v/v) foetal bovine serum (FBS). Thesecells were routinely sub-cultured and used for experimental testing when95% confluent. Adult human dermal fibroblasts were then harvested andre-seeded in DMEM+10% FBS at a cell density of 4×10⁵ cells/ml in a96-well microtitre plate (100 μl/well). The cells were allowed to adhereand spread to the well surface for 24 hours in a humidified incubator at37° C., 5% CO₂. The medium was then removed by aspiration and the cellmonolayer washed with serum-free DMEM. Test samples were then added tothe cell monolayer (100 μl/well), with at least 3 replicates of eachmaterial tested. All test samples were incubated with the cells for 72hours at 37° C., 5% CO₂. After this incubation period a labellingsolution was added from a commercial cell proliferation kit (XTT, CellProliferation kit II, Cat. No. 1 465 015, obtained from BoehringerMannheim). An initial absorbance reading was obtained at 450 nm, and afinal reading taken at 2.5 hrs, the microtiter plate was incubated at37° C., 5% CO₂ during this time. The proliferative effect of each testcondition was evaluated by comparing the absorbance readings measured.By using the positive (10% FBS/DMEM) and negative (Serum free DMEM)control values as 100% and 0% respectively all other conditions could becalculated as a % proliferation.

Test samples included acute and chronic wound fluid, obtained frompatients with either a donor site wound or a chronic venous ulcer,respectively. The wound fluid was collected by aspiration in both cases.

Further experiments were carried out on a simulated wound fluid, whichrepresents the hostile conditions of a chronic wound. The simulatedwound fluid comprised PBS+2% BSA+elastase (5 ug/ml).

All wound fluids were diluted 1:2 with appropriate test samples, i.e.macrophage cell releasates, macrophage cell lysate, monocyte cellreleasate, and incubated for 2 hours at 37° C. prior to addition tofibroblasts. At this point the test samples were further diluted 1:2with serum free DMEM and added directly to the cell monolayer forevaluation in the cell proliferation assay as described above.

Referring to FIG. 1, it can be seen that the fibroblast proliferationfor dermal cell samples (a) and (b) cultured in the chronic wound fluidwas much lower, indeed negative, as compared to the cells (c) culturedin acute wound fluid. This is thought to be due to the presence of highlevels of protease enzymes in the chronic wound fluid that degradegrowth factors and otherwise interfere with cell proliferation.

Referring to FIG. 2, the dermal cells were incubated in (a) 10% serum asa positive control which stimulates cells; (b) serum free medium as anegative control which maintains cells but gives no growth; (c) chronicwound fluid alone; (d) the medium in which the releasate was prepared;(e) both the chronic wound fluid and a monocyte cell releasate; and (f)both the chronic wound fluid and the macrophage releasate.

The results show that the macrophage cell releasate significantlystimulates cell growth and can reverse the negative effect of thechronic wound environment. This effect is significantly better than theobserved effect with the monocyte cell releasate.

Referring to FIG. 3, the samples are (a) 10% serum as a positive controlwhich stimulates cells; (b) serum free medium as a negative controlwhich maintains cells but gives no growth; (c) chronic wound fluidalone; and (d) both the chronic wound fluid and a macrophage celllysate. It can be seen that the macrophage cell lysate sample (d) wasalso able to overcome the negative effect of the chronic woundenvironment and stimulate cell growth.

A similar effect would be achieved with hepatocytes. This is becausemacrophages and hepatocytes both produce a combination of growth factorsand protease inhibitors, primarily alpha-1-antitrypsin.

The above embodiments have been described by way of example only. Manyother embodiments falling within the scope of the accompanying claimswill be apparent to the skilled reader.

1. A wound dressing composition comprising a non-viable cell lysate orreleasate derived from a hepatocyte cell or an inflammatory cell.
 2. Awound dressing composition according to claim 1, wherein the cell lysateor releasate is dispersed in or on a pharmaceutically acceptablevehicle.
 3. A wound dressing composition according to claim 2, whereinsaid pharmaceutically acceptable vehicle is in the form of a solidsheet, a semi-solid ointment, an apertured solid sheet, a web, a wovenfabric, a knitted fabric, a nonwoven fabric, a hydrophilic foam, afreeze-dried sponge or a solvent-dried sponge.
 4. A wound dressingcomposition according to claim 3, wherein said pharmaceuticallyacceptable vehicle comprises a bioabsorbable freeze-dried sponge.
 5. Awound dressing composition according to claim 1, wherein the cellreleasate or lysate is dispersed in or on a solid vehicle thatcomprises, or consists essentially of, a solid bioabsorbable materialselected from the group consisting of collagen, chitosan, oxidizedcellulose, or mixtures thereof.
 6. A wound dressing compositionaccording to claim 1 which is substantially dry.
 7. A wound dressingcomposition according to claim 1, wherein the composition furthercomprises from about 0.01 to about 10% by weight on a dry weight basisof one or more wound healing therapeutic substances.
 8. A wound dressingcomposition according to claim 1 which is substantially sterile.
 9. Awound dressing comprising a wound dressing composition according toclaim
 1. 10. A wound dressing according to claim 9 which is sterile andpackaged in a microorganism-impermeable container.
 11. Use of anon-viable cell lysate or releasate derived from a hepatocyte cell, amacrophage cell, or mixtures thereof, for the preparation of amedicament for the treatment of a wound.
 12. Use according to claim 11,wherein the wound is a chronic wound.
 13. Use according to claim 12,wherein said chronic wound is selected from the group consisting ofvenous ulcers, decubitis ulcers and diabetic ulcers.
 14. A process forthe production of a wound dressing comprising the steps of: lysinghepatocyte or macrophage cells to form a lysate, and dispersing thelysate in or on a pharmaceutically acceptable carrier.
 15. A processaccording to claim 14 further comprising the step, before said step oflysing, of culturing the hepatocyte or macrophage cells in the presenceof an agent selected from the group consisting of cytokines, bacterialendotoxins and exotoxins, and mixtures thereof.
 16. A process accordingto claim 14 further comprising the step of freeze-drying said lysatebefore said step of dispersing.
 17. A process according to claim 15further comprising the step of freeze-drying said lysate before saidstep of dispersing.